Field of the Invention
This invention relates to a by-pass arrangement for controlling the return flow of a pilot valve, which by being connected between the outlet connection from the pilot valve and the return connection to the pilot valve eliminates the return circuit and enables said arrangement to be connected downstream to an open circuit network used for the pulsating delivery of an irrigation liquid. The patents GB 1,286,538, GB 1,484,588, U.S. Pat. Nos. 3,698,195 and 4,009,832 describe localized open-circuit irrigation systems, widely used in agriculture, comprising a pipe directly connected to a feed source (hydraulic pump, pressurized water circuit etc.), from which hoses and secondary pipes of smaller dimensions extend at more or less regular intervals to disperse the liquid over the ground.
These secondary pipes or hoses are themselves variously structured to distribute the liquid as uniformly as possible, even at the points furthest from the source. All comprise pressure release means to cause the liquid to emerge in small quantities (droplets).
With these open circuit systems it is however difficult to achieve uniform irrigation at all points of the ground.
U.S. Pat. No. 4,176,791 describes an irrigation system comprising a pilot valve connected upstream to a pressurized liquid source and from which a succession of pipe sections extends, these being connected together in series by secondary valves provided with a spray nozzle.
The succession of pipe sections starts from the pilot valve and returns to it to form a closed ring.
Although this irrigation system improves the uniformity of liquid distribution over the ground compared with open systems, it is complicated by the use of a double pipe, i.e., an outward pipe and a return pipe to the pilot valve.
In addition, in a closed circuit it is difficult to expel the air which accumulates in the circuit with time and disturbs the correct operation of the valves.
Again, patent application IT 22449A/87 in the name of the present applicant describes a device for automatic pulsating delivery of an irrigation liquid connected downstream to a distribution network provided with valves sensitive to the pressure variations produced by a Venturi device which transmits them to a sliding member.
Said device is complicated by the presence of two counter-pressure membranes, one interposed between said sliding member and the source liquid feed orifice and the other interposed between said sliding member and the bleed orifice to atmosphere. It is the mechanical sliding of the piston and the extreme elasticity of the membranes which enable the valves included in the distribution network to open and close so that the liquid can escape and irrigate the ground.
Even though the system is theoretically usable, its lack of practical usability means that it has been almost completely abandoned.